Abstract
Plasmodium vivax, the second most prevalent of the human malaria parasites, is estimated to affect 75 million people annually. It is very rare, however, in west and central Africa, due to the high prevalence of the Duffy negative phenotype in the human population. Due to its rarity in Africa, previous studies on the phylogeny of world-wide P. vivax have suffered from insufficient samples of African parasites. Here we compare the mitochondrial sequence diversity of parasites from Africa with those from other areas of the world, in order to investigate the origin of present-day African P. vivax. Mitochondrial genome sequencing revealed relatively little polymorphism within the African population compared to parasites from the rest of the world. This, combined with sequence similarity with parasites from India, suggests that the present day African P. vivax population in humans may have been introduced relatively recently from the Indian subcontinent. Haplotype network analysis also raises the possibility that parasites currently found in Africa and South America may be the closest extant relatives of the ancestors of the current world population. Lines of evidence are adduced that this ancestral population may be from an ancient stock of P. vivax in Africa.
Highlights
Plasmodium vivax, responsible for many tens of million cases of malaria globally every year, is the second most abundant malaria parasite of humans after Plasmodium falciparum [1]
Haplotype and nucleotide diversities of worldwide P. vivax populations are shown in Table 2, and give an estimate for the genetic polymorphism of the mitochondrial genome among samples from the six geographical locations considered
Isolates from the Turkey and Iran and those from the Indian sub-continent have comparable haplotype diversities (Turkey plus Iran vs. India, P.0.05), significantly lower than those from East Asia (East Asia vs. India, P = 0.03; East Asia vs. Turkey plus Iran, P = 0.05), and lower, but not statistically significantly so, than those from Melanesia, As expected, diversity was relatively low in South America (P,0.05 for all comparisons, except with Africa), which is generally considered to be the location most recently colonised by P. vivax
Summary
Plasmodium vivax, responsible for many tens of million cases of malaria globally every year, is the second most abundant malaria parasite of humans after Plasmodium falciparum [1] It has the broadest geographic range of the five malaria parasites infective to man, but appears to be almost completely absent in humans from large parts of western and central Africa, where P. falciparum is at its most abundant [2]. One of the alleles of the gene that encodes the DARC protein, FY*Bnull, carries a single nucleotide mutation which impairs promoter activity by disrupting a binding site for the h-GATA-1 erythroid transcription factor [6] This results in the loss of DARC expression on erythrocytes, but does not affect expression in epithelial or endothelial cells. Individuals who are homozygous for this allele express no DARC protein on the erythrocyte surface and so are completely protected from the erythrocytic cycle of P. vivax
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